1. Field of the Invention
The present invention relates to the field of x-ray imaging system. In particular, the invention relates to the use of photon spectra for material discrimination in a single energy x-ray imaging system.
2. Description of Related Art
Material discrimination using x-ray radiation in a number of applications. One example of an x-ray imaging system for material discrimination is the inspection of cargo held in containers to detect target materials such as contraband drugs, illegal weapons, and explosives. To date this has not been demonstrated in practice.
There are a number of prior art techniques that are relevant to material discrimination in cargo inspection.
One technique uses dual energies at low energy. This technique relies on the difference in the photoelectric absorption and Compton scattering as a function of energy and atomic number of the material of interest. This technique is useful in airport security screening but cannot be extended to high energies which are required for cargo scanning.
Another technique is to use single high energy x rays. The high energy spectrum is detected without determining the spectral hardness. This technique merely produces a shadowgraph without characterizing the type of materials causing the shadows.
Another technique, described in U.S. Pat. No. 5,524,133, uses a number of detector configurations to determine the spectral hardness of the beam and from that infer the atomic number of the material that attenuated the beam. This technique is costly requiring extensive detector set-up.
Accordingly, there is a need in the material discrimination technology to have a single-energy x-ray imaging system that is low cost, convenient, and provides fast processing time.